This invention relates to modulators and, more particularly, to a modulator providing for the multiplexing of the directional error signals and the sum signal generated in the tracking feed assembly to provide a single channel for amplification by a receiver which concurrently amplify command signals.
Cross-reference is hereby made to three copending applications pertaining to microwave systems assigned to the same assignee; "Square Conductor Coaxial Coupler" invented by T. Hudspeth, R. V. Basil and H. H. Keeling, Ser. No. 468,826, filed on Feb. 23, 1983; "Coaxial Transmission Line Crossing" invented by T. Hudspeth and H. H. Keeling, Ser. No. 468,827, filed on Feb. 23, 1983; and "Coaxial Line to Waveguide Adapter" invented by T. Hudspeth and H. H. Keeling, Ser. No. 468,825, filed on Feb. 23, 1983. These applications are hereby incorporated by reference in their entirety.
Communication satellites now in use provide communication links among many stations distributed over a large area of the earth. The communication antennas on the satellites may provide beams whose shape matches that of the area served. The communication performance of the satellite is improved when its beams are pointed accurately at the desired directions. The communication beam pointing accuracy is enhanced when ground beacon originating within or near the area served is tracked by the communication satellite antenna. This can be accomplished by embedding a tracking feed network within the communication feed assembly of the antenna, and processing the directional error signals to provide control of the antenna position.
Since two directional error signals and a sum, or reference signal, are generally needed for two-axis control systems, the signal processing is simplified if the microwave error signals are modulated and then multiplexed with the sum signal to provide a complex signal appropriate for amplification in a single channel receiver. It is therefore an object of the invention to attain the foregoing function of signal modulation and multiplexing by use of a ferrite modulator assembly in a structure which simplifies the task of providing a desired redundancy of active elements of the tracking system.